Drosophila neurons are born from progenitors, known as neuroblasts, in a temporally controlled manner. Given that the timing of birth affects the type of neuron that is generated, this process must be tightly regulated over time so that a diverse array of neuronal progeny is produced. The RNA-binding proteins IGF-II mRNA-binding protein (Imp) and 15 Syncrip/hnRNPQ (Syp) are known to exhibit temporally graded expression patterns in neuroblasts, and have thus been shown to regulate the process of neuronal fate specification. Now, on page 3454, Tzumin Lee and colleagues uncover a role for Imp and Syp in neuroblast decommissioning, as well as in neuron differentiation. ‘Decommissioning’ is the process by which neuroblasts shrink and exit the self-renewing progenitor state before forming terminally differentiated neurons. The authors find that Imp and Syp are crucial for this two-stage ‘decommissioning’ process. Imp regulates shrinkage of the neuroblast so that this event does not occur prematurely, while Syp acts subsequently to promote the accumulation of Prospero in the nucleus, leading to cell-cycle exit. Together, these results provide a mechanism by which neuroblast decommissioning occurs in the Drosophila brain and enhance our understanding of how neural stem cells are controlled during development.
